In the past, inter-substrate connectors that directly connect two substrates are used in order to downsize devices and provide additional circuits in a print substrate.
As a method of fixing the two substrates connected by the inter-substrate connectors into a case (a housing), there is a method where screw holes or the like are formed in each of the substrates, and the substrates are fixed one by one to the case. In addition, there is a method where the two substrates are fixed with each other in advance by screwing and then fixed to the case. The latter fixing method is preferably employed when an inspection process is carried out before the two substrates are assembled to the case, or when a small-size subsidiary substrate is fixed on a large-size main substrate.
When the two substrates are fixed with each other in such a manner that the inter-substrate connectors are fitted in advance and then the substrates are fixed by screwing, a stress is caused thereby to twist the inter-substrate connectors due to a rotating moment associated with the screwing. By such a stress, soldered portions of the inter-substrate connecters may be damaged with time.
So, in order to suppress the twisting stress that acts on the inter-substrate connectors, a substrate fixing structure has been proposed. In the structure, the rotating moment directly propagates to the substrates is suppressed by providing a clamping piece and a receiving piece and then fixing one of the substrates so as to clamp the substrate with those pieces (See Patent Literature 1).
In addition, a method where the two substrates are fixed with each other by employing a fixing tool of synthesized resin, without using screws, has been proposed (See Patent Literature 2, Patent Literature 3).
In the fixing structure of Patent Literature 1, more than one small parts are necessary for every screw hole, which may lead to a problem in that assembling procedures become troublesome.
In addition, creep may occur with time in resin parts described in Patent Literature 2 and Patent Literature 3, especially when exposed to a high temperature environment such as a vehicle interior. This may cause backlash, which leads to reduced contact reliability in electrical connection, or to greater vibrating sounds especially in apparatuses mounted in vehicles.